Method of replacing retorts



P 1945- J. A. FOSTER'ET AL 2,372,945

METHOD OF REPLACING RETORTS Filed Aug. 11, 1943 J. A. Foster E. EL Ensign INVENTOR.

Patented Apr. 3, 1945 2,372,946 METHOD OF REPLACING RETORTS John A. Foster, Detroit, and Elbert E. Ensign,

Ypsilanti, Mich, assignors to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Application August 11, 1943, Serial No. 498,212

Claims.

This invention relates to tube furnaces or retorts for the production or refining of materials at high temperatures and low pressures, with particular reference to retort furnaces for the thermal reduction of magnesium ores by the ferrosilicon process.

The object of this invention is to provide a method by which a single tube retort may be changed in a molten bath furnace of the type shown in copending application Serial No. 454,580 without interfering with the operation of the other tubes or shutting down the furnace.

This type of furnace is best exemplified in the production of magnesium by the reduction of dolomitic ores by ferrosilicon under high temperatures and low pressures. The temperatures at which the reaction takes place are well above 2,000" Fahrenheit, and this, together with the very low pressures needed to liberate magnesium vapors, causes deterioration and collapse of the tube retort in conventional gas furnaces. Formerly, the practice was to use a nichrome retort in the gas-fired furnace; but, even these retorts would erode at the temperatures necessary to I maintain the reaction so that the retort life was very short and the process expensive.

It is known that nichrome alloys soften at a lower temperature than that of pure or nearly pure iron. However, the iron is very susceptible to corrosion at the reaction temperatures and it becomes unfit, for, after only a few hours of heating in a gas furnace, this may be overcome by protection given to the retort by submerging it in a molten glass bath'so that oxidation or corrosion can be prevented. In this way erosion was curbed and the superior high-temperature strength of the material utilized. While this has greatly increased the life of the retort, under the loads imposed it will eventually become flat,

bowed and gradually restricted so that efficient,

operation is not obtainable.

In general, each furnace includes a number of individual retorts submerged in one bath, and it is obvious that replacement of a single retort would ordinarily necessitate the complete removal of the molten silicate from the furnace,

withdrawal of the defective tube, replacement The purpose of thi invention,

out interfering with the operation of the remainder of the furnace.

With these and other objects in View, the invention consists in the arrangement, construction and combination of the various parts of the improved device and the steps of the method disclosed, as described in the specification, claimed in the claims and illustrated in the accompanying drawing in which:

Fig. l is a cross-sectional view of a molten bath furnace, showing a defective retort.

Figs. 2, 3, 4 and 5 are'similar cross-sectional views of the furnace, showing the various successive steps in carrying out this invention.

Referring to Fig. 1, the furnace l0 encloses the molten bath II of a silicate or similar substance and has a combustion chamber [2 heated through the gas burner l3 and exhausting through the stack [4. The silicate bath provides an emcient heat-transfer means and'provides protection to the exterior surface of the retort l5 by excluding all oxygen and other corrosive gases. The extreme right end of the retort l5,-which is an auxiliary end section 23 (shown in Figure 5), is omitted in Figures 1-4 as it is usually removed first to cut down the over-all length of the retort which is about to'. be changed. The retort is sup? ported by a solidified silicate seal 16 in the sleeves ll. formed in the furnace well. However, even though corrosion of the tube is prevented, the loads imposed by temperature and the weight of the charge, as well as the hydrostatic pressure of the bath, will eventually deform the retort as shown at l8, and it becomes, as a consequence, increasingly difficult to charge and discharge the furnace. Further, the volumetric capacity is reduced and these disadvantageous factors are soon reflected in the furnace yield. The only adequate remedy is to replace the deformed retort with one which is truly cylindrical.

We are able to replace the deformed retort, while maintaining the furnace at reaction temperature and all other tubes in operation, by the method disclosed. This is accomplished by welding the new retort I9 to the deformed retort I5 at 20 and then heating the seal [6 at each end of the retort by torch 2 I, a shown in Fig. 2, to soften the solidified silicate seal and free the retort l5 from engagement, with the furnace. The combined retorts may then be projected endwardly, as shown by the arrows in Figure 3, but the torch 2! is preferably maintainedin the position shown to heat the new retort prior to its entry in the sleeve I! so that the silicate will not freeze therein. Normally, it is unnecessary to heat the other end further, as the hot tube coming from the bath will prevent freezing. However, by careful control, the silicate in both sleeves may be kept just at the point where it will permit free passage of the retort without appreciable leakage of any of the silicate from the molten bath. Therefore, the torch need only be applied on the outcoming end until the deformed retort has started to move under pressure applied by a crane, jacks or other conventional means.

Thus, in Fig. 3 the old retort I5 is shown par tially drawn out, with the torch 2| used only on the incoming retort ltl and without the loss of any substantial amount of silicate. Even though the silicate bath is molten, its viscosity and surface tension are suificiently high so that its flow through the space between the sleeve and the retort is almost entirely restricted. Similarly it is not necessary to provide a wiping means on the outcoming retort as the internal cohesion of the silicate is greater than the adhesion between the silicate and the retort, so that only very slight film of silicate is deposited on the emerging retort and there is no sleeve leakage of consequence.

Asshown in Fig. 4, after the new retort I9 is drawn into place, the old retort I5 is removed with a flame-cutting torch 22. The silicate seals are then reformed between the furnac and the retort as shown. Usually, cessation of the movement of the pipe and withdrawal of the torch 2| at the entering end encourages freezing at both ends. However, if this is insufiicient,air from a fan or other cooling means directed on the extending parts of the tube adjacent the furnace will speedily cause reformation of a solid seal. Since the pressure within the retor is to be maintained at less than 100 microns, it is extremely important to have the ends of the new retort finished sufiiciently to obtain a tight seal with the'closure used. Any machining of the retort ends after flame-cutting is a difficult operation when the retort remains in the furnace. To avoid this, an auxiliary end section 23 (usually of lighter section), having a finished outer end 24, is welded on the retort I9 at 25. This provides the necessary sealing surface, and, while it maybe difficult to hold the retort to an exact over-all length so that the ordinary type of fixed closure can be used, a special closure disclosed in copending application for Retort construction, Serial'No. 498,210 has been developed which may be used with reasonably varying over-all lengths and minor surface irregularities.

Supporting of the retort within the furnace and the portion withdrawn may be accomplished by conventional means. It is important that, after the retort has started moving through the molten silicate, it should not be stopped until it has been completely withdrawn. In some cases slight axial rotation may be applied to the retort to clear the deformations over internal supports or through the sleeves; but, in general, the latter are large enough to permit unimpeded passage.

.11: is readily seen from the foregoing that a method of this sort is especially advantageous when used in connection with a tube retort furnace in which the heat transfer medium is a molten bath. However, when used with molten baths having low viscosity and high specific heat it may be necessary to maintain a cooling means at the point where the retort projects from the furnace, as shown in copending application Serial No. 471,675. This maintain afluid viscosity high enough so that the molten'material m y be p from running out. On the other hand these baths are usually of such high viscosity that the final step in changing the retort tube entails heating the tube with torches adjacent each sleeve until the bath material becomes sufficiently fluid to fiow to the position indicated-the farthest outward extent of solid material in Fig. 4. The torches are then removed, and the material in the sleeves will solidify almost immediately as shown. This insures a seal of sufficient length to give adequate support to the tube and to prevent leakage of any of the molten material during operation.

Som changes may be made in the arrangement, construction and combination of the various parts of the improved device without departing from the spirit of the invention, and it is the intention to cover by the claims such changes as may be reasonably included within the scope thereof.

The invention claimed is:

The method of replacing a damaged retort tube in a furnace having a plurality of doubleended retort tubes running therethrough and employing as a heating medium a molten bath, said tubes being supported at points at which they pass through the walls'of said furnace by solidified bath material, comprising the steps of welding a replacement retort to one end of and aligned with the retort to be replaced, heating said retort to be replaced at points adjacent the exterior of said furnace to free said retort for movement therethrough, forcing said associated retorts longitudinally through said furnace, thereby replacing said damaged retort with the said replace ment retort, severing the replaced retort from the replacement retort, and controlling the temperature of the associated tubes at the points at which they traverse the walls of said furnace to prevent substantial leakage of the molten material of said bath during the withdrawing operation.

2. The method of replacing a damaged retort in a multi-retort furnace having double-ended retorts extending therethrough and heated by means of a fused bath having a low viscosity and high specific heat, said retorts being supported adjacent their ends by frozen bath material comprising the steps of welding a replacement retort to one end of and aligned with said damaged retort, heating said damaged retort exteriorly of the furnace adjacent its projection through the furnace walls to melt said frozen support and to free the damaged retort for movement relative to said furnace, controlling the temperature of said associated retorts adjacent said furnace walls to prevent the outward fiow of the fused bath while progressively moving said associated retorts longitudinally to replace said damaged re tort with said replacement retort, and thereafter severing said damaged retort from said replacement retort and reforming said frozen supports.

3. The method of claim 2 which incorporates the further step of welding an auxiliary sleeve having a finished outer end to the end of said replacement retort to provide means for a sealing closure therein.

4. The method of claim 2 which incorporates the further steps of heating said replacement retort adjacent the walls of said furnace to flow material from said bath between said replacement retort and said furnace wall until the space therebetween is substantially filled with said material and thereafter permitting said flowed material to solidify. I

5. The method ofreplacing a metal tube traversing adjacent its ends the walls of a furnace containing a bath of molten material, there being substantial clearance between said tube and said walls normally filled by solidified bath material, comprising the steps of welding a replacement tube to one end of the tube to be replaced, melting said solidified bath material to free said first tube, projecting said replacement tube into said furnace thereby ejecting said first tube, and resolidifying bath material in said clearances to fix said replacement tube in place in said furnace.

JOHN A. FOSTER. ELBERT E. ENSIGN. 

